The present invention is generally directed to microfilm recording machines and in particular to an improved automatic exposure control system for automatically adjusting the exposure level to assure proper exposure of each document.
Microfilm recording machines are well known. They find various applications, one application for example being in the banking environment for use in processing checks. During the processing of the checks, each check is photographed on both sides simultaneously onto a reel of microfilm which is then immediately processed or processed when a question concerning an individual check is encountered.
Such microfilm recording machines usually include a document transport for transporting the documents over a predetermined path. Within the predetermined path there is an exposure station which includes an exposure light source and camera to facilitate the photographing of each document as each document is presented to the exposure station. Because the documents generally vary in density or reflective properties, it is necessary to adjust the light output intensity of the exposure light source for each document as each document is recorded. Inasmuch as the documents are processed rapidly, automatic exposure control systems have been devised to rapidly vary the exposure level of the documents as they are phtographed.
While prior automatic exposure controls have been generally successful, they have suffered certain deficiencies. One such deficiency is non-uniform exposure of the documents. This results when an automatic exposure control senses the portion of the document that is being exposed and simultaneously adjusts the illumination level of the exposure light source as the document is being photographed. Also, prior automatic exposure controls have been generally slow in responding to changing required light levels when a light document is immediately preceded by a dark document.
It is therefore a general object of the present invention to provide a new and improved exposure level control system for a microfilm recording machine.
It is a further object of the present invention to provide an automatic exposure control for a microfilm recording machine which adjusts for each document being photographed to assure that each document is photographed at the proper exposure level.
It is a still further particular object of the present invention to provide an automatic exposure control system for a microfilm recording machine which assures a constant and proper exposure level for the photographing of each document.
The present invention provides an automatic exposure control system for use in a document recorder of the type having a document transport for feeding documents along a predetermined path, and an exposure station within the predetermined path including an exposure light source for illuminating each document as each document is presented to the exposure station to facilitate the photographing of the documents, for controlling the illumination intensity of the exposure light source to assure proper exposure of each document. The automatic exposure control system comprises a first light source arranged relative to the predetermined path for projecting light onto the documents to be recorded, a first light sensitive element arranged relative to the predetermined path for receiving the light reflected from the documents originating from the first light source, the first light sensitive element providing a first control signal having a magnitude directly related to the intensity of the reflected light, a feedback arrangement coupled between the first light sensitive element and the first light source for controlling the light output intensity of the first light source responsive to the first control signal to render the intensity of the reflected light received by the first light sensitive element substantially constant, and control means coupled between the first light source and the exposure light source for controlling the illumination intensity of the exposure light source in direct relation to the light output intensity of the first light source.